1. Field of the Invention
The present invention relates to a microprocessor used in a computer system and a memory access method using the microprocessor, and more specifically, to a microprocessor and a memory access method using the same with improved connection flexibility of a memory to be connected.
2. Description of Related Art
In recent years, there have been increasing demands for improving connection flexibility of an external memory connected to a microprocessor or sharing the external memory by a plurality of semiconductor devices in order to construct a computer system with higher flexibility.
Japanese Unexamined Patent Application Publication No. 2006-293591 discloses a system in which a plurality of semiconductor devices share an external memory without a connection of a system bus. This system includes an external memory and a plurality of semiconductor devices, and an interface unit that behaves like an external memory is additionally provided in a first semiconductor device. The interface unit receives a memory control signal output from a memory controller in a second semiconductor device, and transmits an access request to the external memory to the memory controller in the first semiconductor device. Upon receiving the access request, the memory controller in the first semiconductor device outputs a memory control signal to the external memory to access data. According to the system configuration, the plurality of semiconductor devices may share the external memory, and there is no need to include an external memory for each semiconductor device, resulting in cost reduction.
Further, Japanese Unexamined Patent Application Publication No. 2008-129616 discloses a memory control system that allows a memory controller to control an external memory by newly providing a data transfer control apparatus between a memory controller and an external memory even when the external memory employs a different transfer system. The data transfer control apparatus absorbs the difference in the specifications of transfer systems including an SDR transfer system, a DDR transfer system, a bus width doubling transfer system, which allows the memory controller to appropriately control the external memory.